From 3b4da13293482134b81d71be656ec76beff73a76 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Thu, 7 Oct 2021 15:08:29 +0200 Subject: configure: automatically parse command line for meson -D options Right now meson_options.txt lists about 90 options. Each option needs code in configure to parse it and pass the option down to Meson as a -D command-line argument; in addition the default must be duplicated between configure and meson_options.txt. This series tries to remove the code duplication by generating the case statement for those --enable and --disable options, as well as the corresponding help text. About 80% of the options can be handled completely by the new mechanism. Eight meson options are not of the --enable/--disable kind. Six more need to be parsed in configure for various reasons documented in the patch, but they still have their help automatically generated. The advantages are: - less code in configure - parsing and help is more consistent (for example --enable-blobs was not supported) - options are described entirely in one place, meson_options.txt. This make it more attractive to use Meson options instead of hand-crafted configure options and config-host.mak A few options change name: --enable-tcmalloc and --enable-jemalloc become --enable-malloc={tcmalloc,jemalloc}; --disable-blobs becomes --disable-install-blobs; --enable-trace-backend becomes --enable-trace-backends. However, the old names are allowed for backwards compatibility. Message-Id: <20211007130829.632254-19-pbonzini@redhat.com> Signed-off-by: Paolo Bonzini --- docs/devel/build-system.rst | 136 ++++++++++++++++++++++---------------------- 1 file changed, 69 insertions(+), 67 deletions(-) (limited to 'docs/devel/build-system.rst') diff --git a/docs/devel/build-system.rst b/docs/devel/build-system.rst index 0f636d620e..7f106d2f1c 100644 --- a/docs/devel/build-system.rst +++ b/docs/devel/build-system.rst @@ -42,73 +42,21 @@ perform a build: ../configure make -For now, checks on the compilation environment are found in configure -rather than meson.build, though this is expected to change. The command -line is parsed in the configure script and, whenever needed, converted -into the appropriate options to Meson. - -New checks should be added to Meson, which usually comprises the -following tasks: - - - Add a Meson build option to meson_options.txt. - - - Add support to the command line arg parser to handle any new - ``--enable-XXX``/``--disable-XXX`` flags required by the feature. - - - Add information to the help output message to report on the new - feature flag. - - - Add code to perform the actual feature check. - - - Add code to include the feature status in ``config-host.h`` - - - Add code to print out the feature status in the configure summary - upon completion. - - -Taking the probe for SDL2_Image as an example, we have the following pieces -in configure:: - - # Initial variable state - sdl_image=auto - - ..snip.. - - # Configure flag processing - --disable-sdl-image) sdl_image=disabled - ;; - --enable-sdl-image) sdl_image=enabled - ;; - - ..snip.. - - # Help output feature message - sdl-image SDL Image support for icons - - ..snip.. - - # Meson invocation - -Dsdl_image=$sdl_image - -In meson_options.txt:: - - option('sdl', type : 'feature', value : 'auto', - description: 'SDL Image support for icons') - -In meson.build:: - - # Detect dependency - sdl_image = dependency('SDL2_image', required: get_option('sdl_image'), - method: 'pkg-config', - kwargs: static_kwargs) - - # Create config-host.h (if applicable) - config_host_data.set('CONFIG_SDL_IMAGE', sdl_image.found()) - - # Summary - summary_info += {'SDL image support': sdl_image.found()} - - +The configure script automatically recognizes +command line options for which a same-named Meson option exists; +dashes in the command line are replaced with underscores. + +Many checks on the compilation environment are still found in configure +rather than `meson.build`, but new checks should be added directly to +`meson.build`. + +Patches are also welcome to move existing checks from the configure +phase to `meson.build`. When doing so, ensure that `meson.build` does +not use anymore the keys that you have removed from `config-host.mak`. +Typically these will be replaced in `meson.build` by boolean variables, +``get_option('optname')`` invocations, or `dep.found()` expressions. +In general, the remaining checks have little or no interdependencies, +so they can be moved one by one. Helper functions ---------------- @@ -335,6 +283,60 @@ new target, or enabling new devices or hardware for a particular system/userspace emulation target +Adding checks +------------- + +New checks should be added to Meson. Compiler checks can be as simple as +the following:: + + config_host_data.set('HAVE_BTRFS_H', cc.has_header('linux/btrfs.h')) + +A more complex task such as adding a new dependency usually +comprises the following tasks: + + - Add a Meson build option to meson_options.txt. + + - Add code to perform the actual feature check. + + - Add code to include the feature status in `config-host.h` + + - Add code to print out the feature status in the configure summary + upon completion. + +Taking the probe for SDL2_Image as an example, we have the following +in ``meson_options.txt``:: + + option('sdl_image', type : 'feature', value : 'auto', + description: 'SDL Image support for icons') + +Unless the option was given a non-``auto`` value (on the configure +command line), the detection code must be performed only if the +dependency will be used:: + + sdl_image = not_found + if not get_option('sdl_image').auto() or have_system + sdl_image = dependency('SDL2_image', required: get_option('sdl_image'), + method: 'pkg-config', + static: enable_static) + endif + +This avoids warnings on static builds of user-mode emulators, for example. +Most of the libraries used by system-mode emulators are not available for +static linking. + +The other supporting code is generally simple:: + + # Create config-host.h (if applicable) + config_host_data.set('CONFIG_SDL_IMAGE', sdl_image.found()) + + # Summary + summary_info += {'SDL image support': sdl_image.found()} + +For the configure script to parse the new option, the +``scripts/meson-buildoptions.sh`` file must be up-to-date; ``make +update-buildoptions`` (or just `make`) will take care of updating it. + + Support scripts --------------- -- cgit v1.2.3-55-g7522